1. Field of the Invention
This invention relates to a magnetic recording medium comprising a substrate of paper sheet and a method of fabricating it.
2. Description of the Prior Art
Magnetic recording mediums the substrate of which is made of paper sheet have been widely used for tickets for use in automatic ticket gates in railway stations, magnetic sheets (Ricoh, "MY TEACHER", Sonny "TALKING CARD", etc.) for use in teaching machines, because of their mass-productivites and low costs.
Conventional methods of forming a magnetic recording layer on a substrate of paper sheet are enumerated as follows:
(1) a method wherein an organic solvent type or water paint is applied to a substrate of paper sheet;
(2) a method wherein a magnetic tape comprising a plastic base is adhesively put on a substrate of paper sheet; and
(3) a method wherein a magnetic film is applied to a plastic base and then the magnetic film is transferred from the plastic base to a substrate of paper sheet.
The method of the above items (2) and (3) have the advantage that a uniform magnetic film can be provided. However, these methods have the disadvantage that the fabricating costs are comparatively expensive, because they require the intermediate step of making a magnetic tape or the like, as compared with the method of the above item (1).
The method of the above item (1) is extensively used, but it has the essentially unavoidable disadvantage as described below.
According to the method of the above item (1), a magnetic paint containing a solvent is applied and dried to a substrate of paper sheet to form a magnetic film on the substrate. The magnetic film thus formed has a large internal stress. The magnetic film together with the substrate of paper tends to be deformed, for example be curved due to the large internal stress. Since the internal stree of the applied film is primarily caused in course of vaporization of organic solvent or water contained in the paint, this an inevitable problem in case of solvent being used as in the method of the above item (1).
This problem is not important in case of a plastic substrate being used, because the plastic substrate is thermoplastic and therefore even if a deformation is caused, it could easily be eliminated by heating or pressing. However, in case of a paper sheet substrate being used, if a deformation is once caused in the paper sheet substrate, it would be very difficult to eliminate such deformation.
Therefore, an object of this invention is to solve the above-mentioned problems in the prior art and provide a cheap and deformation-free magnetic recording medium using a paper sheet as a substrate.
Another object of this invention is to provide a method of fabricating a cheap and deformation-free magnetic recording medium with a good work efficiency.